Field of the Invention
The present invention relates to a method to detect the charge level of a refrigerant within a refrigeration circuit, where the refrigeration circuit comprises a compressor, a sensor to detect a pressure of the refrigerant and a sensor to detect a temperature, with the method comprising a key cycle that has a first part and a second part.
Description of the Background Art
Within refrigeration circuits a compressor is used to compress a refrigerant, which is circling within the refrigeration circuit. Thus a high pressure side and a low pressure side are created. The compressor needs sufficient lubrication to prevent the compressor from failure.
In an ideal refrigeration circuit the whole lubricant would remain in the compressor to ensure the lubrication of the moving parts of the compressor. In reality the lubricant mixes with the refrigerant, which is compressed by the compressor. The lubricant is discharged out of the compressor with the refrigerant and flows into the remaining refrigeration circuit. The amount of lubricant within the compressor is thus reduced. Typically the lubricant will be transported back into the compressor with the circulating refrigerant.
The physical condition of the refrigerant can be either liquid or gaseous within the refrigeration circuit, where the refrigerant has better transport capabilities for the lubricant in the liquid state than in the gaseous state.
Due to the inevitable loss of the refrigerant from the refrigeration circuit due to leaks or other influences the refrigerant level in the refrigeration circuit can be reduced, which results in a decreased cooling performance. Furthermore a lower level of refrigerant decreases the capability to transport the lubricant through the refrigeration circuit and back to the compressor. At a certain refrigerant charge level the transport capability can be that low that a sufficient lubrication of the compressor cannot longer be maintained. The insufficient lubrication will inevitably lead to compressor damage.
Solutions are known in the conventional art, which use elements to constantly measure the level of refrigerant within the refrigeration circuit to prevent compressor damage. In one application the cycle rate of a cycling clutch orifice tube system is monitored, where lower refrigerant levels will result in faster cycle rates. In another application the system response rates of a variable compressor stroke change is monitored, where lower refrigerant levels will result in faster response rates.
The document DE 199 35 269 C1, which corresponds to U.S. Pat. No. 6,318,097, shows a method to evaluate the charge level of the refrigerant within a refrigeration device, where the temperature and the pressure on the high pressure side is measured periodically and a predetermined temperature value is calculated from a refrigerant specific equation, where the predetermined temperature is subtracted from the measured temperature to obtain a value, from which a conclusion about the refrigerant charge level can be made.
The document U.S. Pat. No. 7,594,407 B2 shows a method to monitor the refrigerant within a refrigeration system, where a saturation temperature of the refrigerant is calculated based on at least one of a discharge pressure and a discharge temperature of the refrigeration device.
The disadvantage of the applications and methods known in the conventional art is that either additional elements such as sensors or orifice tubes are required or that the compressor needs to be a variable stroke compressor. The additional parts and/or the variable stroke compressor make the refrigeration circuit more complex and more expansive.